Diversity is a form of signal reception in which the output signals from two or more independent antennae are combined to provide a signal that is less likely to fade. Various diversity schemes are known in the art. By way of example, various diversity schemes will be discussed in connection with two receive antennae. Each of these diversity schemes is equally applicable to multiple receive antennae.
When there is only one antenna there is no diversity. A no diversity configuration allows for the simplest implementation and results in the lowest power consumption. On the other hand, in the absence of a diversity configuration, the received signal is vulnerable to fading.
In a switched diversity scheme, only one antenna is chosen at any given time during reception. The choice is based on some prescribed selection criterion. The antenna connection is switched when the perceived link quality falls below a certain prescribed threshold.
In a selection diversity scheme, the antenna with the largest signal-to-noise ratio (SNR) or signal power is utilized. The SNR or signal strength measurement can take place during a preamble period at the beginning of a received packet. In this scheme, a single antenna connection is maintained at most times, but both antennae connections are utilized while the SNRs or signal strengths are measured. The actual selection/switching process can take place between packet receptions. The selection process can be done on a packet-by-packet basis or can take place once in a number of receptions or during a prescribed time period.
In a full diversity scheme, both antennae are connected at all times. This mode consumes the largest power as both received paths must be powered up, but also offers the largest performance gain, especially in severe fading environments with large delay spread, compared to other configurations.
In sum, there are various advantages and disadvantages associated with each prior art diversity scheme. These advantages and disadvantages relate to tradeoffs between the quality of the signal reception and the amount of power consumed. For mobile wireless communication devices there are continuing pressures to reduce power consumption. Thus, it would be highly desirable to identify a technique for dynamically selecting a diversity configuration while optimizing signal reception and reducing power consumption.